Remove cell api overrides for lock and unlock

This isn't actually needed as these methods handle objects and is
triggered when the instance object is saved.
It actually caused a race condition with unlock as it triggers 2
instance updates from a compute cell.

Change-Id: I42eea6a2984f70527d4fc37f48ad973a2248721c
Closes-Bug: #1257168
Merge "Remove cell api overrides for lock and unlock"